1. Field of the Invention
The present invention relates generally to position sensors, and, more specifically, to a positioning sensor that determines the position of a conductor contained in a conductive fluid.
2. Background Information
With the increasing popularity of wide area networks (WANs), such as the Internet and/or the World Wide Web, network growth and traffic has exploded in recent years. Network users continue to demand faster networks and more access for both businesses and consumers. As network demands continue to increase, existing network infrastructures and technologies are reaching their limits.
An alternative to present day hardwired or fiber network solutions is the use of wireless optical communications. Wireless optical communications utilize point-to-point communications through free space and therefore do not require the routing of cables or fibers between locations. Thus, wireless optical communications are also known as free space or atmospheric optical communications. For instance, in a free space optical communication system, a beam of light is directed through free space from a transmitter at a first location to a receiver at a second location. Data or information is encoded into the beam of light, and therefore, the information is transmitted through free space from the first location to the second location.
An important aspect of a free space optical communications system is tracking. In particular, it is important that the optical communications beam (e.g., laser beam) is aimed properly from the transmitter at the first location and that the receiver at the second location is aligned properly to receive the optical communications beam. For example, assume that a transmitter is mounted on a first building and that a receiver is mounted on a different second building. Assume further that there is a line of sight between the transmitter and receiver. It is important for the transmitter on the first building to be configured to accurately direct or aim the optical communications beam at the receiver on the second building.
Tracking is utilized for maintaining the alignment of the optical communications beam between the transmitter and receiver in various situations or disturbances. Examples of these various situations or disturbances include the swaying of the buildings due to for example windy conditions, vibration of the platforms on which the transmitter and/or receiver are mounted, atmosphere-induced beam steering, etc. If the tracking system is unable to compensate for disturbances, the optical communications beam is no longer properly aimed at the receiver and, consequently, communications between the transmitter and receiver are lost or impaired.
The present invention provides an apparatus and method for determining a position and/or orientation of a conductor disposed in a conductive fluid. A plurality of electrodes disposed about the conductor and preferably being in contact with the conductive fluid are used to provide an electrical path between each electrode and the conductor. In one embodiment, resistances between each electrode and conductor are determined through use of a signal processing circuit. In another embodiment, capacitances between each electrode and the conductor are determined using a similar signal processing circuit. Once the resistances or capacitances are determined, the position of the conductor can be determined based on these values in combination with parameters relating to the configuration of the electrodes and conductor, as well as characteristics of the conductive fluid. In one implementation, the invention may be used in free space optical communication systems, whereby the position of the end portion of the fiber optic cable can be determined.
According to a first aspect of the invention, the apparatus comprises a plurality of electrodes that are fixedly disposed relative to a cavity containing the conductive fluid. In one embodiment, the plurality of electrodes are configured as a leading set of coplanar electrodes disposed on one end of the conductor, and a trailing set of coplanar electrodes disposed toward the other end of the conductor. In one configuration each of the leading and trailing sets of coplanar electrodes are radially arrayed about the cavity using substantially equal angles between each pair of radially-adjacent conductors. In one implementation of this configuration, there are three leading and three trailing electrodes. In one embodiment, the apparatus further comprises means for measuring resistances between each electrode and the conductor. In another embodiment, the apparatus includes means for measuring capacitances between the electrodes and the conductor. The apparatus further comprises a processing means for determining the position and/or orientation of the conductor based on the resistance or capacitive values that are determined.
In one embodiment, the means for measuring the resistances and processing means are provided by a signal processing circuit that includes a first multiplexer that receives a reference voltage as an input that is multiplexed to each of the electrodes in the leading set of electrodes via respective leads connected to those electrodes. A second multiplexer, having a plurality of multiplexed inputs that are connected to respective leads for each of the electrodes in the trailing set is then used to multiplex electrical paths between the conductor and the trailing set of electrodes. Using both of the multiplexers, electrical paths between any electrode in the leading set and any electrode in the trailing set can be established. Voltages corresponding to these multiplexed electrical paths are then received by an analog-to-digital converter, which produces digitized data corresponding to the voltages. This digitized data is then processed by the processing means, which typically may comprise a digital signal processor, an ASIC, a microcontroller, or other type of processor. In general, the position of the conductor can be determined by solving a set of equations with the processing means based on the configuration of the electrodes and other parameters discussed above. For example, in the implementation comprising three leading and three trailing electrodes, a six-by-six matrix corresponding to six simultaneous equations may be solved to determine the values for each resistance or capacitance. Once these values are known, further processing is performed to yield the position and/or orientation of the conductor.
According to other aspects of the invention, methods are provided for determining the position and/or orientation of the conductor based on the foregoing apparatus embodiments.